<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>1_js输出</title>
</head>

<body>
  <script>
    // 控制浏览器弹出一个警告窗
    alert('123');
    // 输出内容到页面上
    document.write('345');
    // 输出内容到控制台
    console.log('456');
  </script>
</body>

</html>